I am newbie to C. I have a csv file with a particular structure. I created struct and and read the data from csv file and print it using defined struct. However, instead of printing the struct I need to save it so I an access it for later processing. So far, I have understood I need to use dynamic memory allocation but I am totally lost right now. any leads would be really useful.
The inputfile as follows,
2,33.1609992980957,26.59000015258789,8.003999710083008
5,15.85200023651123,13.036999702453613,31.801000595092773
8,10.907999992370605,32.000999450683594,1.8459999561309814
11,28.3700008392334,31.650999069213867,13.107999801635742
14,7.046000003814697,23.5939998626709,6.254000186920166
My code so far
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct O_data
{
unsigned int index;
float x;
float y;
float z;
};
struct O_data * deserialize_data(struct O_data *data, const char *input, const char *separators)
{
char *p;
struct O_data tmp;
if(sscanf(input, "%d,%f,%f,%f", &data->index, &data->x, &data->y, &data->z) != 7)
return NULL;
return data;
}
int main(int argc, char *argv[])
{
FILE *stream;
char *line = NULL;
size_t len = 0;
ssize_t nread;
struct O_data somedata;
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
exit(EXIT_FAILURE);
}
stream = fopen(argv[1], "r");
if (stream == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
while ((nread = getline(&line, &len, stream)) != -1) {
deserialize_data(&somedata, line, ",");
// How do I save some data to memory here to access it later like somedata[i] for ith struct later outside main.
printf("index: %d, x: %f, y: %f, z: %f\n", somedata.index, somedata.x, somedata.y, somedata.z);
}
free(line);
fclose(stream);
exit(EXIT_SUCCESS);
}
// How do I save some data to memory here to access it later like somedata[i] for ith struct later outside main.
you can use an array of struct O_data using malloc then realloc to allocate then make longer that array having an unknown number of entries until you read all the file
Warning in deserialize_dat
sscanf(input, "%d,%f,%f,%f", &data->index, &data->x, &data->y, &data->z)
index is unsigned but you use %d, must be %u, it is the same in printf in main
tmp and p are unused, like the parameter separators
A proposal can be :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct O_data
{
unsigned int index;
float x;
float y;
float z;
};
struct O_data * deserialize_data(struct O_data *data, const char *input)
{
return (sscanf(input, "%u,%f,%f,%f", &data->index, &data->x, &data->y, &data->z) != 7)
? NULL : data;
}
int main(int argc, char *argv[])
{
FILE *stream;
char *line = NULL;
size_t len = 0;
ssize_t nread;
struct O_data * somedata = NULL;
size_t nelts = 0;
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
exit(EXIT_FAILURE);
}
stream = fopen(argv[1], "r");
if (stream == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
while ((nread = getline(&line, &len, stream)) != -1) {
if ((somedata = realloc(somedata, (nelts + 1) * sizeof(struct O_data))) == NULL) {
fprintf(stderr, "error not enough memory");
exit(EXIT_FAILURE);
}
deserialize_data(&somedata[nelts++], line);
}
free(line);
fclose(stream);
/* print and free */
for (size_t i = 0; i != nelts; ++i)
printf("index: %u, x: %f, y: %f, z: %f\n",
somedata[i].index, somedata[i].x, somedata[i].y, somedata[i].z);
free(somedata);
exit(EXIT_SUCCESS);
}
Compilation and execution :
pi@raspberrypi:/tmp $ gcc -pedantic -Wall -Wextra a.c
pi@raspberrypi:/tmp $ cat f
2,33.1609992980957,26.59000015258789,8.003999710083008
5,15.85200023651123,13.036999702453613,31.801000595092773
8,10.907999992370605,32.000999450683594,1.8459999561309814
11,28.3700008392334,31.650999069213867,13.107999801635742
14,7.046000003814697,23.5939998626709,6.254000186920166
pi@raspberrypi:/tmp $ ./a.out f
index: 2, x: 33.160999, y: 26.590000, z: 8.004000
index: 5, x: 15.852000, y: 13.037000, z: 31.801001
index: 8, x: 10.908000, y: 32.000999, z: 1.846000
index: 11, x: 28.370001, y: 31.650999, z: 13.108000
index: 14, x: 7.046000, y: 23.594000, z: 6.254000
Execution under valgrind :
pi@raspberrypi:/tmp $ valgrind ./a.out f
==2439== Memcheck, a memory error detector
==2439== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==2439== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==2439== Command: ./a.out f
==2439==
index: 2, x: 33.160999, y: 26.590000, z: 8.004000
index: 5, x: 15.852000, y: 13.037000, z: 31.801001
index: 8, x: 10.908000, y: 32.000999, z: 1.846000
index: 11, x: 28.370001, y: 31.650999, z: 13.108000
index: 14, x: 7.046000, y: 23.594000, z: 6.254000
==2439==
==2439== HEAP SUMMARY:
==2439== in use at exit: 0 bytes in 0 blocks
==2439== total heap usage: 9 allocs, 9 frees, 5,832 bytes allocated
==2439==
==2439== All heap blocks were freed -- no leaks are possible
==2439==
==2439== For counts of detected and suppressed errors, rerun with: -v
==2439== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)
Note I realloc adding only one entry in the array each time, if there are a lot of values in the file it can be better to add several entries rather than just one in the realloc when needed